Valves are used for blocking or establishing a controlled volume flow of a working fluid, or rather, of a liquid or gaseous fluid, or pressurizing medium, in virtually all technical fields in which fluids are used for transmission and/or storage of energy. They are applicable both in power conduits and in control conduits of pressurizing media driven control systems or regulating units and in this respect enable directly as well as indirectly the operation of pressurizing media driven actuators of all types in general; hydraulic control conduits differ from hydraulic power conduits essentially by their smaller cross section. As examples for such actuators servomotors, pumps, engines, compressors, clutches, brakes, and hydraulic or pneumatic springs, gears, and linkages are mentioned. In this respect, valves not only are of fundamental functional importance within hydraulic or pneumatic systems. Due to their varied application an essential portion of costs for manufacturing and maintenance of such systems falls to them, too.
In hydraulic drives, the driving power is known to be controlled by the pressure and the flow rate of a working fluid conducted in a circuit from a reservoir, usually in the form of an oil pan, via the delivery side of a motor-driven pump to a hydraulic consumer and from this back to the reservoir on the low-pressure side. The pump is usually a hydraulic pump with constant or variable delivery volume, such as a screw pump or a radial piston pump that is driven by an electric motor. As consumers are used servomotors and hydraulic motors respectively for generation of a translatory or rotatory output movement; the former may be configured as hydraulic cylinders, the latter as gear motors. For controlling the volume flow of the working fluid to and from the hydraulic consumer a control device with valves is provided in this connection in the flow path between the pump and the consumer. The working fluids controlled that way are preferably fluids on the basis of mineral oil, so-called hydraulic oils, synthetic fluids, or fluids on the basis of plants, wherein the latter being characterized particularly by its environmental compatibility. These working fluids can contain additives that permit a selective influencing of individual characteristics, such as the thermal characteristic, the aging resistance, or the corrosiveness.
Conventionally, each valve used in such a control device comprises a housing with a guide region and with borings, which form an inlet opening, an outlet opening, and a control opening of the particular valve, and a shut-off body in the form of a piston. The piston is in each case supported for sliding co-operation in the guide region of the housing and movably guided between an open-position, in which the valve is open and enables a flow connection between the inlet opening and the outlet opening, and a close-position, in which the valve is closed and prevents a flow connection between the inlet opening and the outlet opening. In addition, each of the valves has a retaining means between the housing and the piston usually comprising a compression spring and biasing the piston in each case in a defined rest position, hence in its open- or close-position.
Corresponding to the particular hydraulic flow scheme of the control device for a hydraulic drive, each of the valves is connected with its inlet opening, outlet opening, and control opening by a flow connection with the flow path for conducting the working fluid. As flow connections, or rather, tubing connections for conducting the working fluid within such a fluid system in principle all flow connections known to be suitable come into question, hence both rigid tubing elements, such as pipes or recesses in a housing of a particular element of the system, and flexible tubing elements, such as flexible tubes, wherein the particular flow connections can be made, for instance, of metal and/or plastic. Flow connections in the form of borings or other pre-formed recesses made, for instance, by metal casting in a part of a housing are frequently used, in particular in mechanical and in automotive engineering, since they cannot only be produced as to particularly low space requirements in virtually any pipe geometry, but they notably can be configured in compliance with the particular requirements to be considered as to stability, or rather, pressure and leak tightness without any difficulty, too.
In this regard, a control device for a hydraulic drive shall be mentioned exemplarily that controls the working fluid flow from a reservoir to the hydraulic drive and from the latter back to the reservoir. Such a control device usually comprises a so-called valve block which is formed in a way as specified and has between at least one inlet port and one outlet port a flow connection with in each case one control valve for controlling the working fluid flow in the supply and discharge of the hydraulic consumer, and one or several pilot control valves for activating the two control valves, if applicable, and the related flow connections in the form of hydraulic power conduits and control conduits for the hydraulic coupling of the valves as intended. The valve block typically is made of solid metal configured as cube-shaped housing and comprises, in addition to the recesses for the flow connections, recesses for receiving the particular valves. These recesses usually are realized as blind holes or milled-out portions in the valve block and either form the housing of the particular valve directly, wherein the inner surface of the recess comprises the guiding region, or the seat for a usually cupular or tubular valve housing formed separately. Whereas a recess having a surface finish obtainable by drilling or milling mostly suffices to be used as a seat for a separately formed valve housing, direct use of a recess in the valve block as guiding region for a piston movable between its close- and open-position implies in any case appropriate surface finishing, for instance by roller-burnishing, grinding, lapping, and/or honing, to ensure the valve function as required. A control device for a hydraulic elevator configured accordingly is disclosed, for instance, in U.S. Pat. No. 4,637,495. The valve block specified there on the one hand comprises valves with their particular guiding region being directly formed in the valve block, where the valve block thus constitutes the housing with the particular guiding region and in this respect is encompassed by the particular valve as functional part, too. On the other hand, however, this known valve block comprises also valves with separate cupular housings. For these valves the valve block thus merely constitutes a suitable valve seat with the necessary flow connections, whereas the particular valve forms a functional unit completely separated from the valve block in other respects.
Valves of these two embodiments are generally applicable in all of the afore-mentioned technical fields and are not limited to the specific use stated in U.S. Pat. No. 4,637,495. Their adaption to the particular field of application primarily is carried out by an appropriate selection of the individual valve components with regard to geometry and material as well as by an appropriate dimensioning of retaining force of the retaining means, thus in this respect merely by an appropriate setting of the valve parameters in terms of the kind of working fluid to be controlled, the volume of the working fluid flow, and the pressure prevailing in the flow path with the valve structure unchanged in other respects. With those valve designs disclosed in U.S. Pat. No. 4,637,495, it is possible insofar to control volume flows of nearly all common working fluids at working fluid pressures usually prevailing within the particular fluid system, be it of a hydraulic or of a pneumatic type.
However, each of the two valve designs has disadvantages. So it is a disadvantage of the valve design with the guiding region for the movable piston directly formed in the valve block that this essential valve component has to be custom-made with the valve block, per se ruling out a cost-efficient large-scale production. The considerably higher surface quality required in any case for a guiding region of a valve in comparison to the rest of the recesses in the valve block is only attainable by additional process steps during manufacturing of the valve block as, namely, by roller-burnishing, grinding, lapping, and/or honing. Hence, this additional effort in manufacturing of the valve block on the one hand entails higher manufacturing costs for the valve block itself, and on the other hand higher manufacturing costs for the valve. Another major disadvantage of this valve design is that damage of the guiding region, which may be caused for instance by metallic foreign particles as a consequence of normal wear and tear during operation of the control device or by corresponding contaminants in the working fluid used, possibly may only be repaired by replacement of the entire valve block. Therefore, a valve of this embodiment not only is expensive in production, but insofar cost-intensive in operation, or maintenance, too.
The latter disadvantage, in fact, can be remedied by using a separate valve housing of the kind of the second valve design disclosed in U.S. Pat. No. 4,637,495, since such a valve in case of damage readily can be replaced without also replacing the valve block at the same time. The disadvantage of high production costs, however, also applies for such a valve in fact insofar as the required quantity of material and the machining effort during the manufacturing of the cupular or tubular valve housing are high. Because irrespective of whether the recess of the valve housing for sliding co-operation with the piston is made of a rod material, e.g. by drilling or milling, or of a pipe material, the valve housing still extends essentially over the entire length of the valve. In order to enable movement of the piston, and the valve function thereby, the valve housing must have appropriate openings in addition. These openings are generally produced individually in the wall of the housing in accordance with the particular intended use of the valve in a further manufacturing step typically by drilling or milling. A further process step is finally required to provide the inner surface of the valve housing with the necessary surface finish for the guiding region so that the piston can slidably co-operate with the guiding region in its movement between its close- and open-position. As already stated above, this process step for the surface finishing is usually carried out by roller burnishing, grinding, lapping, and/or honing. For a cylindrically shaped piston as illustrated in U.S. Pat. No. 4,637,495 generally the entire inner surface of the cupular or as a hollow cylinder formed valve housing is machined in this way in the region of the lateral area of the cylinder adjacent to the piston. Simply because of the cost of materials and the type and scope of process steps required for manufacturing the valve housing, production of such a valve is complex and cost-intensive with a substantial proportion of the production costs particularly being attributable to the fabrication of the valve openings.
It is therefore the problem of the invention to set forth a valve which is suitable for blocking or establishing of a controlled volume flow of a working fluid in a flow path of a technical device for transmission and/or storage of energy, particularly in a control device for a hydraulic drive, and which overcomes the disadvantages of the prior art, that therefore has its own valve housing having a guiding region which can be manufactured in a simpler and cheaper way, which additionally is designed easier to maintain, and is cheaper in operation and maintenance, and which ultimately can be manufactured also in a cost-saving way, in particular, within the bounds of large-scale production. Furthermore, the invention relates to a process for the manufacturing of such a valve and to a hydraulic apparatus for a working fluid with a particular embodiment of the inventive valve.